The present invention relates generally to a semiconductor memory device.
A semiconductor memory device refers to a memory device embodied by using a semiconductor such as silicon Si, germanium Ge, gallium arsenide GaAs, indium phospide Inp, etc. The semiconductor memory device is classified into a volatile memory device or a non-volatile memory device.
The volatile memory device has a characteristic where stored data is lost if power is not supplied. Examples of volatile memory devices include a static RAM SRAM, a dynamic RAM DRAM, a synchronous DRAM SDRAM and so on. The non-volatile memory device has a characteristic where stored is not lost even if power is not supplied. Examples of non-volatile memory devices include a read only memory ROM, a programmable ROM PROM, an electrically programmable ROM EPROM, an electrically erasable and programmable ROM EEPROM, a flash memory, a phase-change RAM PRAM, a magnetic RAM MRAM, a resistive RAM RRAM, a ferroelectric RAM FRAM, etc. The flash memory device is further classified into a NOR-type memory device or a NAND-type memory device.
A memory cell array of a semiconductor memory device such as a flash memory device is supplied high voltage when a program operation and an erase operation are performed. Accordingly, as the program/erase cycle increases, the deterioration of the memory cell array of the semiconductor memory device increases. Deterioration of the memory cells leads to reduced reliability within the stored data, which in return leads to reduced reliability of the entire semiconductor memory device.